Observation of concurrent mass enhancement and superconductivity in a topological state

Low energy, laser-based ARPES is used to examine the temperature dependence of a topological state previously reported^1,2 for the Fe-based superconductors, FeSe_xTe_1-x. In the present study of the same system at temperatures below the superconducting transition we observe the concurrent onset of mass enhancement at the Dirac point, suggestive of time reversal symmetry breaking, and the appearance of the superconducting gap at the Fermi level crossing. We discuss possible explanations for the coincident presence of these two gaps below T_c. At the same time, focusing on the Dirac state provides some evidence for increased robustness of superconductivity in the surface layer.

¹Zhang et al., Science 360, 182 (2018)
²J.D. Rameau et al., (submitted)